Blowdown of cryogenic liquid supply vessel



Feb. 28, 1967 E. sco'r'r ETAL 3,306,061

BLOWDOWN 0F CRYOGENIC LIQUID SUPPLY VESSEL Filed Aug. 23, 1965 LYN/V E. 50077 0'00 JOSEPH KLE/NHAUT INVENTORS ATTORNEY United States Patent Ofilice 3,3fl6fifil Patented Feb. 28, 1967 3,306,061 BLOWDOWN F CRYOGENIC LIQUID SUPPLY VESSEL Lynn E. Scott, Westfieid, and Joseph Kieinhaut, Livingston, N.J., assignors to Air Reduction Company, Incorporated, New York, N.Y. a corporation of N ew York Filed Aug. 23, 1965, Ser. No. 431,860 2 Ciaims. (Cl. 6255} This invention relates to the blow-down of a supply vessel containing a liquefied gas and more particularly to an improved method and apparatus for increasing the liquid yield obtained in the fluid discharged from a liquefied gas container during pressure reduction and discharge thereof.

The advantages of storing and transporting gas in a liquefied state are well known. In those instances wherein the fluid is to be utilized in vapor form, various arrangements are available for eflecting a complete vaporization of the liquid, whereby all of the liquid is exhausted from the container. In numerous applications, however, it is necessary to make available the withdrawn fluid in a liquid state. Present methods and apparatus available for this purpose result in a relatively low liquid recovery from the storage container.

The present invention is directed to an improved method and apparatus which result in a significant increase in the amount of liquid obtained in the fluid discharged from the liquefied gas container. While the invention has broad utility in this field, it is particularly useful for the blowdown of cryogenic fluids and is especially advantageous for accumulation of a liquid fraction by the pressure reduction of liquefied helium containers.

An object of this invention is the provision of an improved method and apparatus for increasing the liquid yield obtained in fluid discharged from a pressurized liquefied gas container during discharge.

An object of this invention is the provision of a method of obtaining a greater liquid recovery from a liquefied gas container during discharge of the container by a throttled expansion of the fluid.

An object of this invention is the provision of an improved method of discharging a cryogenic fluid from a container having an elevated pressure, the discharged fluid being desired in a liquid state and at a reduced pressure.

An object of this invention is the provision of improved apparatus for use in discharging a liquefied gas container, said apparatus producing an increased liquid yield in the discharged fluid upon expansion and partial liquefaction thereof.

An object of this invention is the provision of improved discharging apparatus in combination with a container having a cryogenic fluid at an elevated pressure, which combination is constructed and arranged to produce an increased liquid yield upon partial liquefaction of the fluid discharged.

These and other objects and advantages of the invention will become apparent from the following description when taken with the accompanying drawings. It will be understood, however, that the drawings are for purposes of illustration and are not to be construed as defining the scope or limits of the invention, reference being had for the latter purpose to the claims appended hereto.

In the drawings wherein like reference characters denote like parts in the several views:

FIGURE 1 is a diagrammatic illustration of apparatus made in accordance with this invention; and

FIGURE 2 is a similar fragmentary illustration of apparatus made in accordance with the prior art.

Reference now is made to FIGURE 1, wherein the reference numeral identifies a storage container, such as a trailer-mounted tank, containing the liquefied gas, say, helium, at an elevated pressure. A discharge line 11 extends from the storage tank and into a liquid-accumulating vessel, such as a Dewar flask 12. Inserted in the line 11 is a Joule-Thompson throttling valve 13. The Dewar flask 12 is vented through a second line 14, which is arran ed in heat exchange relation to the line 11, the heat exchanger being identified by the numeral 15.

The blow-down of a vessel at an elevated pressure, the fluids content of which is at a temperature above the normal boiling point, results in a lowering of temperature (due to a throttled expansion) and is accompanied by a partial liquefaction of the discharged fluid. The liquid is withdrawn through the line 11 and a liquid-vapor separation takes place in the Dewar flask, with the vapor exiting through the line 14. The vapor passes through the heat exchanger which pre-cools the fluid, in a highly eflicient and advantageous manner, prior to its passage through the valve 13. Such cooling of the fluid, after its discharge from the container and prior to its expansion, increases the liquid yield obtained from the expanded fluid, as will now be explained.

As liquid is withdrawn, the material and energy balance around the heat exchanger 15 (FIGURE 1), assuming no heat leak, is expressed by the following standard equations.

1 z=( 4 a) and, since isenthalpic expansion takes place at the valve 13,

2 L+( 3 where:

X=the fraction of fluid passing the valve 13 which is produced as liquid in the Dewar flask down stream of the valve 13,

lz =enthalpy of the fluid after leaving the storage container 10 and on entering the heat exchanger,

lz =enthalpy of the fluid leaving the heat exchanger and before entering the valve,

h =enthalpy of the saturated liquid produced in the Dewar flask after Joule-Thompson expansion,

h =enthalpy of the saturated vapor exiting from the Dewar flask and entering the heat exchanger,

h =enthalpy of the vapor leaving the heat exchanger,

(1-X) =fraction vapor produced after expansion and vented from the Dewar flask to the heat exchanger.

Substituting the value for h in Equation 1, we obtain:

On the other hand, in the case wherein there is a direct expansion of the fluid, as shown in FIGURE 2, that is, without the heat exchange arrangement of this invention,

h =Xh +(1X)h or s 1. where:

X=fraction of liquid produced in the Dewar flask, as

liquid produced in the heat exchange system of FIGURE 1), it will be assumed that:

(a) The temperature T; of helium vapor leaving the heat exchanger is 0.5 R. lower than the temperature T Applying the above values in Equation 3,

h4 h n-m,

= 0.6434 fraction liquefied downstream of the value Similarly, in the case wherein there is a direct expansion of the liquid from the tank, as shown in FIGURE 2, 25 the gas enthalpy values are,

Applying the above values in Equation 5,

r h 5 h:h1,

=0A571 fraction liquefied downstream of the value Therefore, the increase in liquid fraction by using the heat exchange system of this invention is,

X (with heat exchanger) =0.6434

X (without heat exchanger) increased liquid fraction 5 A liquid increase of better than 18% is obtained when the pressure in the storage container is p.s.i.a. and, obviously, there will be no increase when the container pressure is equal to that of the Dewar flask. However, it can be shown, mathematically, that the increased yield at a storage container pressure of 25.2 p.s.i.a. is 2.4%.

The invention is not restricted to the continuous liquid withdrawal from the Dewar flask, as specifically shown and described herein. Similar desiderata apply to an arrangement for batch accumulation of liquid from the receiving vessel as, for example, by the elimination of a draw-off line 16 shown in dotted lines in FIGURE 1. Also, the expansion of the liquid can be done in several steps with a heat exchanger inserted between the steps.

Having now described the invention, those skilled in this art will be able to make various changes and modifications without thereby departing from the spirit and scope of the invention as set forth in the following claims.

We claim:

1. A method of increasing the liquid yield obtained in the fluid discharged from a vessel containing a cryogenic fluid at an elevated pressure comprising, discharging fluid from the vessel, throttling said discharged fluid to produce liquid and vapor, accumulating the liquid and the vapor in a second vessel at a pressure substantially below said elevated pressure, venting only the vapor from said second vessel, and cooling said discharged fluid before throttling with said vented vapor.

2. In combination, a storage vessel containing a cryogenic fluid at an elevated pressure, a heat exchanger, a second vessel for reception of a cryogenic liquid at a pressure substantially below said elevated pressure, a discharge line connected between said first-mentioned vessel and said heat exchanger, said heat exchanger directing fluid to said second vessel from said discharge line, a throttling valve connected to the heat exchanger and receiving said fluid therefrom, said second vessel having a vapor vent and accumulating liquid and vapor discharging from said valve, and a vapor directing line connected between the said vent and the heat exchanger, the recited arrangement being such that the fluid passing through the heat exchanger is cooled by heat exchange contact with the vapor exiting from said second vessel before said fluid passes through said throttling valve.

References Cited by the Examiner UNITED STATES PATENTS 2,033,094 3/1936 De Motte 6255 2,632,302 3/1953 Steele 6255 3,048,021 8/1962 Coles et al. 625l4 LLOYD L. KING, Primary Examiner. 

1. A METHOD OF INCREASING THE LIQUID YIELD OBTAINED IN THE FLUID DISCHARGED FROM A VESSEL CONTAINING A CRYOGENIC FLUID AT AN ELEVATED PRESSURE COMPRISING, DISCHARGING FLUID FROM THE VESSEL, THROTTLING SAID DISCHARGED FLUID TO PRODUCE LIQUID AND VAPOR, ACCUMULATING THE LIQUID AND THE VAPOR IN A SECOND VESSEL AT A PRESSURE SUBSTANTIALLY BELOW SAID ELEVATED PRESSURE, VENTING ONLY THE VAPOR FROM SAID SECOND VESSEL, AND COOLING SAID DISCHARGED FLUID BEFORE THROTTLING WITH SAID VENTED VAPOR. 